Optoelectronic signal recording medium and method of making same

Abstract

An optoelectronic signal recording and storage medium including a base layer, a conductive layer, a photoconductive layer and storage layer has a coherent crystal morphology throughout, even though the chemical and electrical properties of its layers are by choice dramatically different. The base layer is preferably made of monocrystalline sapphire grown in a manner as to allow the growth of the other layers directly on a surface of the base layer without the need to grind and polish that surface, thereby minimizing internal defects in the medium. The monocrystalline base layer also allows the acceptance of exeptionally uniformly distributed charges over wide areas of the medium, thereby enabling the medium to locally record and store minutely differing optoelectronic signals on a background of minimal noise, thus facilitating low light level electronic or optical recording and long term storage of signals and minimal energy readout of those stored signals. The medium base layer can be thin enough to be flexible and transparent and yet to have great strength to provide a firm foundation for the other medium layers. A method of making the medium is also disclosed.

What is claimed as new and desired to be secured by Letters Patent of the United States is: PG,79 
     
       1. In a plural layer optoelectronic recording medium in sheet or strip form of the type including a base layer having a surface and a light modulating layer added to said surface of the base layer the improvement wherein the base layer is a thin monocrystal of an inorganic material and whose crystal orientation and surface perfection are such as to enable the growth on said surface of a thin light modulating layer composed of an inorganic crystalline material with a very high degree of perfection from nucleation sites on said surface so that the entire medium has a coherent crystal morphology. 
     
     
       2. The medium defined in claim 1 wherein said medium also includes a thin dual-material dielectric storage layer added on top of said modulating layer and whose atomic lattice arrangement is compatible with those of said other medium layers and which stores a light image focussed onto it as a distribution of coulombic charge domains has anisotropic electrical properties regarding mobility of charge carriers in the storage layer. 
     
     
       3. The medium defined in claim 2 wherein said storage layer includes and interfacial zone adjacent to said modulating layer for inhibiting movements of charge carriers. 
     
     
       4. The medium defined in claim 1 wherein said modulating layer includes at least one electrically conductive zone adjacent to said base layer to form an electrode. 
     
     
       5. The medium defined in claim 1 wherein said base layer is transparent to light energy from ultraviolet to far infrared and the modulating layer is absorbtive to light over that same energy spectrum. 
     
     
       6. The medium defined in claim 1 wherein said base layer consists of monocrystalline sapphire. 
     
     
       7. The medium defined in claim 1 wherein said medium is highly flexible and spoolable. 
     
     
       8. A plural layer optoelectronic recording medium in sheet or strip form comprising A. a thin base layer consisting of a single web-like monocrystalline sapphire crystal whose surfaces are substantially defect free and having a surface;   B. a thinner inorganic conductive layer grown as a crystal on said surface of the base layer from nucleation sites on said surface so that the conductive layer has a crystal arrangement that is compatible with that of said base layer and has a high degree of perfection;   C. a thin photoconductive layer added as a continuum on top of said conductive layer and being capable of electrically modulating an incident light image; and   D. a thin dual-material storage layer added integrally on top of said photoconductive layer for capturing electronic charge carriers from said photoconductive layer and thereby storing an electrical analog of said incident light image.   
     
     
       9. The medium defined in claim 8 wherein said base layer and conductive layer are transparent to light energy and the photoconductive layer absorbs incident light energy. 
     
     
       10. The medium defined in claim 9 wherein said medium is very flexible and spoolable. 
     
     
       11. The medium defined in claim 9 wherein all of said layers in the medium have compatible atomic lattice thereby forming a coherent hetero-epitaxially grown structure. 
     
     
       12. An optoelectronic recording tape comprising A. a thin, flexible, optically clear substrate;   B. a conductive layer covering the substrate and for connection electrically to voltage applying means;   C. a photoconductive layer covering the conductive layer; and   D. a dual-material dielectric storage layer covering the photoconductive layer, said storage layer including (1) an interfacial zone covering the photoconductive layer, and   (2) a storage zone for exposure to an electron cloud, said interfacial zone permitting the tunnelling through it of photogenerated charges from the photoconductive layer during exposure of the tape under the influence of a strong electrical field resulting from the deposition of electrons from electron generating means on the surface of the storage zone and the application of voltage to the conductive layer whereby said charges are trapped at anisotropic storage positions in the undersurface of said storage zone.     
     
     
       13. An optoelectronic recording tape as defined in claim 12 wherein said interfacial zone also inhibits electrical charges generated in said photoconductive layer after tape exposure when an electric field is not present from reaching said storage zone and upsetting the count of photogenerated charges trapped thereat during exposure of the tape. 
     
     
       14. The method of making an optoelectronic recording medium comprising the steps of A. forming a monocrystalline substrate layer as a very thin sheet or tape with a minimum number of internal lattice defects and with a high degree of surface perfection;   B. growing a monocrystalline conductive layer or zone on a surface of said substrate layer from nucleation sites on said surface so as to continue the atomic spacing and internal perfection of the substrate layer; and   C. growing a monocrystalline photoconductive light modulating layer or zone on said conductive layer so as to propagate the lattice arrangement and internal perfection of said conductive layer or zone thereby forming a hetero-epitaxially grown sheet or tape structure which is coherent with respect to its crystal morphology, but is layered or stratified with respect to its electrical and chemical characteristics.   
     
     
       15. The method defined in claim 14 and including the additional step of adding a dual-material dielectric storage layer to the exposed surface of the photoconductive layer so that the storage layer has an internal structure that is compatible with the photoconductive layer crystal lattice. 
     
     
       16. The method defined in claim 15 wherein the dualmaterial storage layer is added with a sufficiently high degree of perfection that it is chargable electrically with exceptional uniformity. 
     
     
       17. The method defined in claim 15 wherein the thicknesses of said layers are controlled so that one of said dielectric layer and said substrate layer is transparent and said medium is flexible enough to be rolled up into a small diameter roll. 
     
     
       18. The method defined in claim 15 wherein each successive layer added to the substrate layer is deposited at a temperature lower than the one needed to produce the previous layer and all deposition temperatures are sufficiently low as not to melt or otherwise disturb the substrate layer. 
     
     
       19. The method defined in claim 14 wherein the thicknesses of the substrate layer and conductive layer are controlled so that those layers are transparent to light energy over a wide spectral range.